Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $185.48   10.727%   $205.3764   $205.38   $205.40   $205.40  
  Purchase #2 $221.66   6.124%   $235.2345   $235.23   $235.25   $235.20  
  Purchase #3 $237.71   11.801%   $265.7622   $265.76   $265.75   $265.80  
  Purchase #4 $168.71   5.678%   $178.2894   $178.29   $178.30   $178.30  
  Purchase #5 $230.44   5.331%   $242.7248   $242.72   $242.70   $242.70  
  Purchase #6 $59.85   5.393%   $63.0777   $63.08   $63.10   $63.10  
  Purchase #7 $152.80   10.799%   $169.3009   $169.30   $169.30   $169.30  
  7 purchase totals = $1,256.65       $1,359.7659   $1,359.76   $1,359.80   $1,359.80